Any structure may suffer damage during its use that may lead to the eventual failure of the structure. In many scenarios, it is important to monitor damage so that the damage can be repaired or the structure can be replaced before any failure or degradation of performance occurs. Many such structures are built and used in the aeronautical, aerospace, maritime, or automotive industries.
When damage occurs within a structure, the damaged area emits a sound or acoustic emission (AE) that propagates through the material of the structure. Damage monitoring systems, in the form of acoustic emission detection and monitoring systems, have been provided that detect the acoustic emission made as damage occurs to a structure. The acoustic emissions are detected by sensors attached at known locations in the structure. The time of flight (ToF) of the acoustic emission to each sensor is recorded. The location of the AE can then be determined using triangulation of the ToFs for a given AE from the known locations for the receiving sensors.
However, acoustic emissions may travel at different velocities through different parts of a structure depending on its structural properties. In other words, the propagation of an acoustic emission through a structure can be considered to be non-linear. Thus the mechanical properties of the material from which the structure is formed, such as the density, modulus of elasticity and Poisson coefficient, have an effect on the velocity of an AE. Furthermore, structural features such as changes in thickness, material boundaries or voids also have an effect on the velocity and propagation path of an AE. Such variation in the propagation of AEs through structures reduces the accuracy to which an AE event can be located using existing acoustic emission detection and monitoring systems.